Wave-Powered Glider Delivers Your Message In A Bottle

Setting a bottle adrift with a message in it is, by most measures, an act of desperation. The sea regularly swats mighty ships to their doom, so what chance would a tiny glass bottle have bobbing along the surface, subject as it is to wind, waves, and current? Little to none, it would seem, unless you skew the odds a bit with a wave-powered undersea glider to the help the bottle along.

Before anyone gets too worked up about this, [Rulof Maker]’s “Sea Glider” is about a low-tech as a device with moving parts can be. This craft, built from a scrap of teak and a busted wooden ruler, is something that could be assembled in a few hours from whatever you have on hand, even if you’re marooned on an uncharted desert isle. The body of the craft sprouts a set of horizontal planes that can swivel up and down independently. The key to providing a modicum of thrust is that each plane is limited to a 90° swing by stop blocks above and below the pivot. The weighted glider, tethered to the bottle, bobs up and down below the waves, flapping the planes and providing a tiny bit of thrust.

Was it enough to propel the bottle any great distance? We won’t ruin the surprise, but we will say that [Rulof]’s essentially zero-cost build appears to have improved the message in a bottle bandwidth at least somewhat. It’s not a Hackaday Prize-winning robotic sea glider, but it’s a neat hack nonetheless.

Hydrogen balloons that work this way were discussed during the American Civil War. The idea was to alternately let off gas and ballast and a large plane or “wing” is positioned on the gondola like the planes on the device described here.

It seems to me that the unit would benefit from some kind of orientation control. …perhaps magnetizing he weight on the bottom and making a compos out it…simple for going along magnetic north/south lines…more complex at other angles but might still be doable if the iron can be magnetized enough at all.